This invention relates to a microelectromechanical systems (MEMS) thermal device, and its method of manufacture. More particularly this invention relates to a MEMS thermal switch for switching electrical signals.
Microelectromechanical systems (MEMS) are very small moveable structures made on a substrate using lithographic processing techniques, such as those used to manufacture semiconductor devices. MEMS devices may be moveable actuators, valves, pistons, or switches, for example, with characteristic dimensions of a few microns to hundreds of microns. A moveable MEMS switch, for example, may be used to connect one or more input terminals to one or more output terminals, all microfabricated on a substrate. The actuation means for the moveable switch may be thermal, piezoelectric, electrostatic, or magnetic, for example.
FIG. 1 shows an example of a prior art thermal switch, such as that described in U.S. Pat. No. 7,036,312, to Menard, et al. The thermal switch 10 includes two cantilevers, 100 and 200. Each cantilever 100 and 200 contains a passive cantilevered beam 110 and 210, respectively. A conductive circuit 120 and 220, is coupled to each cantilevered beam 110 and 210 by a plurality of dielectric tethers 150 and 250, respectively. When a voltage is applied between terminals 130 and 140, a current is driven through conductive circuit 120. The Joule heating generated by the current causes the circuit 120 to expand relative to the unheated cantilevered beam 110. Since the circuit is coupled to the cantilevered beam 110 by the dielectric tether 150, the expanding conductive circuit drives the cantilevered beam in the upward direction 165.
Applying a voltage between terminals 230 and 240 causes heat to be generated in circuit 220, which then drives cantilevered beam 210 in the direction 265 shown in FIG. 1. Therefore, one beam 100 moves in direction 165 and the other beam 200 moves in direction 265. These movements may be used to open and close a set of contacts located on contact flanges 170 and 270, each in turn located on tip members 160 and 260, respectively. For example, driving cantilever 100 in direction 165, then driving cantilever 200 in direction 265, relaxing cantilever 100 and then relaxing cantilever 200 may serve to close the switch, by engaging contact flanges 170 and 270. In this position, contact between the faces of contact flanges 170 and 270 provides an electrical connection between cantilevers 100 and 200, such that in FIG. 2d, the electrical switch is closed. Opening the electrical switch is accomplished by reversing the movements in the steps described above.